Electrical conditions near the bases of thunderclouds over New Mexico

Measurements of atmospheric electricity were made at a mountain‐top observatory with some instruments at the earth's surface and with others carried aloft by captive balloons into the bases of thunderclouds overhead. The properties measured included the charge on individual precipitation particles, the electric current density carried by precipitation, the local electric field vector, and the electrical conductivity of the air. The electric fields aloft, near cloud base, were often twice the intensity of the surface fields and had large horizontal components that indicated non‐uniform distributions of charge. The polar electrical conductivity of cloudy air was found to be about 2 times; 10 −15 per ohm m which is about 1/10 that of the clear air at the same altitude. The polarity of charge on the precipitation aloft was almost invariably that of the local potential gradient; it did not show the well‐known ‘mirror‐image’ relation that is observed between the precipitation electricity at the ground and the local potential gradient during periods of point discharge. Use of our charge and conductivity data in Wormell's analysis of Wilson's ion capture mechanism suggests that ion capture in the subcloud region may explain adequately the precipitation charge arriving at the earth. There was little correlation between the magnitudes of the precipitation charge aloft and the intensity of the electric field. We could not identify the origin of the charges found on precipitation aloft although one possible explanation is that they were derived from that residing on the cloud droplets from which the raindrops were formed. Calculations of the electrical power transfer in the lower regions of developing thunderclouds by the fall of charged precipitation indicate local energy dissipation as predicted by Vonnegut, with rates of about 5 times; 10 −6 watts m −3 .